Use of carbon nanomaterials produced with low carbon footprint to produce composites with low CO2 emission

ABSTRACT

A low carbon footprint material is used to decrease the carbon dioxide emission for production of a high carbon footprint substance. A method of forming composite materials comprises providing a first high carbon footprint substance; providing a carbon nanomaterial produced with a carbon-footprint of less than 10 unit weight of carbon dioxide (CO 2 ) emission during production of 1 unit weight of the carbon nanomaterial; and forming a composite comprising the high carbon footprint substance and from 0.001 wt % to 25 wt % of the carbon nanomaterial, wherein the carbon nanomaterial is homogeneously dispersed in the composite to reduce the carbon dioxide emission for producing the composite material relative to the high carbon footprint substance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority and/or benefit from U.S.Provisional Patent Application Ser. No. 62/752,124, filed Oct. 29, 2018,entitled “Massively amplified carbon cycle GHG CO2 removal with C2CNTcarbon nanotubecomposites”, U.S. Provisional Patent Application Ser. No.62/890,719, filed Aug. 23, 2019, entitled “Massively amplified carboncycle GHG CO2 removal with C2CNT carbon nanotube-composites”, andInternational Application No. PCT/US2019/058674, filed Oct. 29, 2019,entitled “Use of carbon nanomaterials produced with low carbon footprintto produce composites with low CO2 emission”, the entire contents ofeach of which are incorporated herein by reference.

FIELD

The present invention relates to use of carbon nanomaterials producedwith low carbon footprint to produce composites with low CO₂ emissionand related methods.

BACKGROUND

Structural materials, such as cement, metal, or the like, are useful invarious applications and industries. For example, cement and metal areuseful for the construction of buildings, bridges, and roads; and metalsare useful for the production of vehicles and industrial and consumerappliances. A suitable structural material for a particular applicationmay require certain mechanical strength and other physical properties,which can place limitations on the design and cost of a givenconstruction project or product. The pervasive use of structuralmaterials is a substantial contributor to global carbon dioxideemissions and climate change. Additives to structural materials can formcomposites, alloys or admixtures with improved, desirable properties,laminates, insulators, or drywall can form composites, alloys oradmixtures with improved, desirable properties.

It is often desirable to enhance the properties of a structural materialthrough additives to form composites, alloys or admixtures withimproved, desirable properties. Examples of desirable properties includetensile, compressive and flexural strength and durability. In a similarmanner, additives to other materials such as electrical conductors,glass, ceramics, paper, resin, polymer, or plastics, cardboardlaminates, insulators, or drywall can form composites, alloys oradmixtures with improved, desirable properties, Examples of desirableproperties include electrical conductivity or insulation, thermalconductivity or insulation, small volume or weight, fracture resistance,flexibility and strength.

Additives to form composites with enhanced, desirable properties, canalso have drawbacks which include technical complexity, such complexityof forming the composite, lack of desired properties in the additive, orinhomogeneity of the additive, or complexity of scale-up, or scarcity ofthe additive making the composite cost prohibitive, and increased carbondioxide emissions in their production contributing to global carbondioxide emissions and climate change. Furthermore, production of thevirgin structural material, or electrical conductors, glass, ceramics,paper, polymer, resin plastics, cardboard laminates, insulators, ordrywall is often associated with a large carbon footprint. For example,typical stainless steel production has a carbon footprint of 6.15 tonnesof emitted CO₂ per tonne of steel produced. Aluminum productiontypically emits 11.9 tonnes of CO₂ per tonne of product; titaniumproduction typically emits 8.1 tonnes of CO₂ per tonne of product;magnesium production typically emits 14 tonnes of CO₂ per tonne ofproduct and copper production typically emits 5 tonnes of CO₂ per tonneof product. It is often desirable to form a material with a reducedcarbon footprint. A reduced carbon footprint emits less greenhouse gascarbon dioxide. Carbon dioxide contributes to climate change, which hasadverse effects including global warming, sea level rise, drought,flooding, severe weather events, economic loss, adverse health effectsand habitat loss and species extinction.

SUMMARY

The present disclosure relates to methods of combining a high carbonfootprint substance, such as structural materials, such as cement,metal, wood or the like, or electrical conductors, glass, ceramics,paper, polymer or plastics, cardboard laminates, insulators, or drywall,to form a composite with a low carbon footprint, readily mixed,industrially scaleable, cost effective carbon nanomaterials to reducethe carbon dioxide emission for producing the composite materialrelative to the high carbon footprint substance.

In an aspect, there is provided a method of forming lowered carbonfootprint materials, comprising providing a first high carbon footprintsubstance to be converted to a composite with improved property (orproperties); providing a material comprising a carbon nanomaterialproduced with a carbon-footprint of less than 10 unit weight of carbondioxide (CO₂) emission during production of 1 unit weight of the carbonnanomaterial; and forming a composite comprising the first structuralmaterial and from 0.001 wt % to 25 wt % of the carbon nanomaterial,wherein the carbon nanomaterial is homogeneously dispersed in thecomposite.

In the method of the preceding paragraph, the carbon-footprint may be 1to 10, or 0 to 1. The carbon-footprint may be negative, which mayindicate net consumption of carbon dioxide during the production of thecarbon nanomaterial. The carbon nanomaterial may comprise straightcarbon nanotubes that do not entangle for ready dispersion in thecomposite. The carbon nanomaterial may comprise carbon nanofibers. Thecarbon nanofibers may have an average aspect ratio of 10 to 1000 and athickness of 3 nm to 999 nm. The nanofibers may comprise carbonnanotubes. The nanofibers may comprise helical carbon nanotubes. Thecarbon nanofibers may comprise untangled carbon nanofibers. The carbonnanomaterial may comprise carbon nano-onions. The carbon nanomaterialmay comprise a carbon nano-scaffold. The carbon nanomaterial maycomprise a nano-platelet. The carbon nanomaterial may comprise graphene.The method may comprise adding the reinforcing material to a solidphase, a liquid phase, or a gas phase, of the structural material toform the composite. The method may comprise dispersing the carbonnanomaterial in a liquid to form a first mixture, admixing the firstmixture with the structural material to form a second mixture, andforming the composite from the second mixture. The liquid may comprisewater. The carbon nanomaterial may be formed from a molten carbonate byelectrolysis. The molten carbonate may be generated by reaction ofcarbon dioxide and a metal oxide in a molten electrolyte. The metaloxide may be a lithium oxide. The molten carbonate may comprise alithium carbonate, a lithiated carbonate or an alkali and/or alkaliearth carbonate mix. The structural material may comprise cement,concrete, mortar, or grout. The structural material may comprise ametal, such as one or more of aluminum, steel, magnesium, and titanium.The structural material may comprise a plastic material. The structuralmaterial may comprise a polymer. The structural material may comprisewood. The structural material may comprise a cardboard. The structuralmaterial may comprise a laminate. The structural material may comprise adrywall. Other high carbon footprint substances may comprise a resin, aceramic, a glass, and insulator or an electrical conductor. The carbonnanomaterial may have domain sizes less than 1,000 μm in the composite.The composite may comprise 0.01 wt % to 1 wt %, or 0.01 wt % to 0.5 wt%, or 0.01 wt % to 0.3 wt %, or 0.01 wt % to 0.1 wt %, of the carbonnanomaterial.

In another aspect, there is provided a composite produced according to amethod described herein.

In a further aspect, there is provided use of a carbon nanomaterialproduced with a carbon-footprint of less than 10 unit weight of carbondioxide (CO₂) emission during production of 1 unit weight of the carbonnanomaterial, for reinforcing a structural material.

In a further aspect, there is provided use of a carbon nanomaterial in acomposite comprising a structural material to reinforce the structuralmaterial, wherein the carbon nanomaterial is produced with acarbon-footprint of less than 10 unit weight of carbon dioxide (CO₂)emission during production of 1 unit weight of the carbon nanomaterial.

In a further aspect, there is provided use of a carbon nanomaterialproduced with a low carbon-footprint in a composite comprising astructural material and the carbon nanomaterial, for reducing overallemission of carbon dioxide (CO₂) during the manufacture of thecomposite, wherein the low carbon-footprint is a carbon-footprint ofless than 10 unit weight of CO₂ emission during production of 1 unitweight of the carbon nanomaterial. The carbon nanomaterial may beproduced from a molten carbonate by electrolysis. The composite may be acomposite described herein.

Other aspects and features of the present invention will become apparentto those of ordinary skill in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures, which illustrate, by way of example only, embodiments ofthe present invention,

FIG. 1A is a scanning electron microscope (SEM) image of sample carbonnanotubes produced from a molten carbonate by electrolysis;

FIG. 1B is photographic image of a glass container containing a mixtureof water and carbon nanotubes homogeneously dispersed in water;

FIG. 1C is a photographic image of a composite material formed from themixture of FIG. 1B;

FIG. 2 is a schematic block diagram illustrating an example productionprocess for producing a composite of a structural material and a carbonnanomaterial, according to an embodiment of the present disclosure;

FIG. 3 is a block diagram illustrating the challenges of structuralmaterial-carbon nanomaterial composite pathways to lower carbonfootprint structural materials, and the removal of hurdles to greenerstructural materials;

FIG. 4 is a block diagram of an electrolysis system to produce carbonnanomaterials from molten carbonate and carbon dioxide;

FIG. 5 comprises photographs of building the 2 tonne CO2 dailyconversion C2CNT plant;

FIG. 6 shows a Raman spectra of sample carbon nanotubes;

FIG. 7 shows a Raman spectra of sample carbon nano-onions;

FIG. 8 shows Raman spectra samples of graphene and carbon platelets;

FIG. 9 shows a sample carbon nano-scaffolds;

FIG. 10 shows a sample helical carbon nanotubes;

FIG. 11 shows a sample of a laminate carbon nanomaterial component; and

FIG. 12 shows cement and aluminum examples of the CO₂ reduction throughthe addition of carbon nanotubes.

DETAILED DESCRIPTION

It has been recognized that carbon nanomaterials can be used to formcomposites with enhanced properties. However, conventional carbonnanomaterials are produced with a large carbon footprint, are formed athigh cost, and generally form twisted, tangled materials not conduciveto the homogeneous dispersion requisite of high quality composites. Todate the large (commercial) production of carbon nanomaterials has beenaccomplished by variants of chemical vapor deposition (CVD) synthesis.For example, a typical conventional technical for producing carbonnanotubes (CNTs) utilizes CVD synthesis. CVD synthesis of CNTs generallyproduces twisted and tangled CNTs which are not conducive to simplemixing. Entangled and twisted CNTs tend to agglomerate in an aqueousmixture, and are thus difficult to be dispersed homogeneously into thecomposites based on water mixtures, such as cement or concrete. Unevendistribution of CNTs within the cement or concrete will compromiseproduct integrity and reduce the efficient utilization of thereinforcement material. CVD synthesis utilizes expensive organometallics(or mixtures of metals and organics), at dilute concentration and veryhigh energy. This requires a high expense of preparation and results ina high market cost (for example upwards of $100,000 per tonne for CNTs,and upwards of $1,000,000 per tonne for graphene. Therefore it would notbe practical and economical to use carbon nanotubes produced by CVD toproduce composites. Furthermore, a CVD process also has a large carbonfootprint, for example, emitting up to 600 tonnes of CO₂ for producingone tonne of carbon nanomaterials (V. Khanna, B. R. Bakshi, L. J. Lee,J. Ind. Ecology, 12 (2008) 394-410). As used herein, the term “carbonfootprint” of a particular product generally refers to the amount ofcarbon dioxide (CO₂) emitted during production of the particularproduct. The expression “carbon-footprint”, denoted F_(c), is usedherein to represent a specific metric of the carbon footprint, F_(c)=thenumber of unit weight of CO₂ emitted during production of one unitweight of the product. F_(c) can be calculated as the weight ratio ofthe total CO₂ emitted during production and the particular productproduced during production, F_(c)=(weight of CO₂ emitted duringproduction)/(weight of produced product). Hence CVD has acarbon-footprint of approximately F_(C)=600. A further technicalchallenge in producing composites of cements and carbon nanofibers suchas carbon nanotubes (CNTs) is that CNTs produced by CVD can be highlyentangled and tend to agglomerate in an aqueous mixture and are thusdifficult to be dispersed homogeneously into the concrete. Unevendistribution of CNTs within the concrete will compromise productintegrity and reduce the efficient utilization of the reinforcementmaterial.

A low carbon footprint carbon nanomaterial may be produced from a moltencarbonate by electrolysis, at low cost and using CO₂ as a reactant, forexample as C2CNT (CO₂ to Carbon Nanotube) synthesis. However technicalchallenges had prevented scale-up of the process and the materialremains scarce. While, examples of C2CNT CNTs had been termed“straight,” each example of synthesized, grouped, CNTs shown was visiblyentangled, and twisted or hooked, although less twisted than CNTsdenoted “tangled”. Entangled and twisted CNTs tend to agglomerate, andare thus difficult to be dispersed homogeneously in a composite. In theC2CNT examples straight referred specifically referred to CNTscontaining less sp³ bonding amongst carbons defects and tangled CNTscontain more sp³ defects. Example processes for producing carbonnanomaterials from molten carbonates by electrolysis are disclosed in,for instance, Licht et al., “Transformation of the greenhouse gas CO₂ bymolten electrolysis into a wide controlled selection of carbonnanotubes,” J. CO ₂ Utilization, 2017, vol. 18, pp. 335-344; Ren et al.,“One-pot synthesis of carbon nanofibers from CO₂ ,” Nano Lett., 2015,vol. 15, pp. 6142-6148; Johnson et al., “Carbon nanotube wools madedirectly from CO₂ by molten electrolysis: Value driven pathways tocarbon dioxide greenhouse gas mitigation,” Materials Today Energy, 2017,pp. 230-236; Johnson et al., “Data on SEM, TEM and Raman Spectra ofdoped, and wool carbon nanotubes made directly from CO₂ by moltenelectrolysis,” Data in Brief, 2017, vol. 14, pp. 592-606; Ren et. al.,“Tracking airborne CO₂ mitigation and low cost transformation intovaluable carbon nanotubes,” Scientific Reports, Nature, 2016, vol. 6,pp. 1-10; Licht et al., “Carbon nanotubes produced from ambient carbondioxide for environmentally sustainable lithium-ion and sodium-ionbattery anodes,” ACS Cent. Sci., 2015, vol. 2, pp. 162-168; Dey et al.,“How does amalgamated Ni cathode affect carbon nanotube growth? Adensity functional theory study,” RSC Adv., 2016, vol. 6, pp.27191-27196; Wu et al., “One-pot synthesis of nanostructured carbonmaterial from carbon dioxide via electrolysis in molten carbonatesalts,” Carbon, 2016, vol. 106, pp. 208-217; Lau et. al., “Thermodynamicassessment of CO₂ to carbon nanofiber transformation for carbonsequestration in a combined cycle gas or a coal power plant,” EnergyConvers. Manag., 2016, vol. 122, pp. 400-410; Licht, “Co-production ofcement and carbon nanotubes with a carbon negative footprint,” J. CO ₂Utilization, 2017, vol. 18, pp. 378-389; Ren et al., “Transformation ofthe greenhouse gas CO₂ by molten electrolysis into a wide controlledselection of carbon nanotubes,” J. CO ₂ Utilization, 2017, vol. 18, pp.335-344; Licht et al., “A new solar carbon capture process: solarthermal electrochemical photo (STEP) carbon capture,” J. Phys. Chem.Lett., 2010, vol. 1, pp. 2363-2368; Licht, “STEP (Solar ThermalElectrochemical Photo) Generation of Energetic Molecules: A SolarChemical Process to End Anthropogenic Global Warming,” J. Phys. Chem. C,2009, vol. 113, pp. 16283-16292; Wang et al., “Exploration of alkalication variation on the synthesis of carbon nanotubes by electrolysis ofCO₂ in molten electrolytes,” J. CO ₂ Utilization, 2019, vol. 34, pp.303-312; Liu et al., “Carbon nano-onions made directly from CO₂ bymolten electrolysis for greenhouse gas mitigation,” Adv. SustainableSyst., 2019, vol. 3, 1900056; Licht et al., “Amplified CO₂ reduction ofgreenhouse gas emissions with C2CNT carbon nanotube composites,” Mater.Today Sustainability, 2019, vol. 6, 100023; U.S. Pat. No. 9,758,881 toLicht, entitled “Process for electrosynthesis of energetic molecules;”U.S. Pat. No. 9,683,297 to Licht, entitled “Apparatus for molten saltelectrolysis with solar photovoltaic electricity supply and solarthermal and heating of molten salt electrolysis;” US 2019/0039040 toLicht, entitled “Methods and systems for carbon nanofiber production;”WO2016/138469 to Licht et al., entitled “Methods and systems for carbonnanofiber production;” WO2018/093942 to Licht, entitled “Methods andsystems for production of elongated carbon nanofibers;” andWO2018/156642 to Licht, entitled “Methods and systems for production ofdoped carbon nanomaterials.”

In brief overview, an aspect of the present disclosure is related toprocesses of producing with reduced carbon dioxide emissions a compositewherein the composite high carbon footprint substance formed with a lowcarbon footprint, readily dispersible a carbon nanomaterial (CNM). Priorto the work described herein, it was thought that CNMs were only massproduced with a high carbon footprint at high cost, and in a tangledmatter. Low carbon footprint CNMs could be produced, but were alsotangled, could not be dispersed uniformly in a composite, and were notmass produced. Surprisingly, it was found that low carbon footprint CNMscould be produced in an untangled manner, low cost, mass produced, andreadily dispersed within a high footprint substance forming a low carbonfootprint composite.

Conveniently, carbon nanomaterials produced from a molten carbonate byelectrolysis can be produced with a relatively low carbon footprint anda relatively low cost, as compared to carbon nanomaterials produced byother conventional techniques such as chemical vapor deposition (CVD)synthesis, flame synthesis, or plasma synthesis. Here, low cost refersto (i) the cost relative aluminum production, which costs less than$2,000 per tonne, and (ii) to the cost such that the CNM additive costalone does not comprise more than the cost of the virgin, high carbonfootprint substance alone used in the composite. Here, high cost refersto a cost such as over $100,000 or over $1,000,000 per tonne such as istypical of CNMs commercial production by chemical vapor deposition.

However, prior molten carbonate produced CNMs provided technicalchallenges to scale-up, such as scale-up to industrial dimensionelectrodes, high current interconnects compatible with high temperaturemolten carbonates, and management of the CO2 gas reactant in industrialconditions. Furthermore, all prior molten syntheses produced CNMs thatwere tangled, twisted or overlapping. Such tangling, twisting oroverlapping is a technical barrier to the facile separation and uniform,homogeneous dispersion of CNMs requisite for a homogeneous composite.

As shown in FIG. 1A, new conditions of the molten carbonate electrolysisproduces CNMs that do not tangle, twist or overlap. The production ofCNMs by molten carbonate electrolysis permits substantial control overthe CNM product by control of electrolysis conditions such as electrodematerial choice, electrolyte compositions, and temperature. As shown inFIG. 1A, new conditions of a 740° C. electrolyte composed (by wt %) of73% Li₂CO₃, 17% Na₂CO₃, and 10% LiBO₂, using a Muntz Brass cathode andan Inconel anode produce uniform, straight carbon nanotubes. Thescanning electron microscope (SEM) image of the CNT product is shown.The CNT product is produce at high coulombic efficiency of 97.5% (97.5%of the applied charge results in CNT mass in accord with the 4 electronreduction of CO₂).

The untangled CNTs of FIG. 1A were hydrophobic, but were readily,uniformly dispersed in water facilitated by a short duration ofsonication. Upon mixing the aqueous suspension of homogeneouslydispersed CNTs with Portland cement, the resulting admixture was readilycast into CNT-cement composites, 0.048 wt %, of the produced CNTs wasadded to Portland cement to form the CNT-cement composite. It wasobserved that less than 0.75 unit weight of the composite could providethe same mechanical strength as 1 unit weight of the pure cement, areduction in mass by at least 25%. The mass reduction of the highfootprint substance, cement, formed by composite with same strength lowfoot print CNM, requires less cement to produce, reducing the carbondioxide emission for producing the composite material relative to thehigh carbon footprint substance.

In a preferred embodiment, a high carbon footprint substance is combinedwith a low carbon footprint carbon nanomaterial forming a composite withreduced carbon dioxide emission relative to the high carbon footprintsubstance. In a preferred embodiment that low carbon footprint carbonnanomaterial is industrially scaleable, and produces untangle carbonnanomaterials. In a further preferred embodiment that high carbonfootprint substance is a structural material, such as cement, metal,wood or the like. In a further preferred embodiment that high carbonfootprint substance is electrical conductors, glass, ceramics, paper,polymer or plastics, cardboard laminates, insulators, or drywall.

A “low carbon footprint” herein refers to a carbon footprint withF_(c)≤10. Processes or products produced with no CO₂ emission or with anet consumption of CO₂ are also considered to have a low carbonfootprint, where F_(c)≤0.

Producing CNM from molten carbonate by electrolysis consumes CO₂ as thereactant, and thus has a negative carbon footprint.

It has been recognized by the present inventors that the above-noteddrawbacks of high costs, negative environmental impact, and technicaldifficulties likely all contributed to the limited utilization of carbonnanomaterials produced by CVD and other similar conventional techniquesin commercial and industrial applications.

When carbon nanomaterials are added to a structural material such asconcrete or a metal structure, the resulting composite material can haveimproved mechanical properties such as improved tensile, compressive andflexural strength. For example, it has been demonstrated that carbonnanotubes (CNTs) have a tensile strength of up to about 93,900 MPa andadding a small amount, such as less than 0.05 wt %, less than 0.8 wt %,or less than 1 wt %, of CNTs to cement can produce carbonnanotube-cement (CNT-cement) composites with much improved mechanicalproperties. For example, tensile, compressive, and flexural strengths ofthe composite may be higher than those of the virgin cement, such as by45% in a typical case.

FIG. 2 illustrates an example process S10 according to an embodiment ofthe present disclosure.

As illustrated, a high carbon footprint substance is provided at S12.The substance, as an example, may be a structural material that is usedprimarily to provide a physical structure or support a physicalstructural in view of the material's mechanical properties, as opposedto its other properties such as electrical, magnetic, electromagnetic,or chemical properties. Common structural materials include concrete,cement, mortar, grout, metals such as steel, aluminum, iron, magnesium,titanium, or alloys, wood, paper board or cardboard, plastic materials,composites, or the like. It is noted that in some applications, astructural material may be selected in view of its other properties inaddition to its mechanical properties.

The structural material provided at S12 may be obtained, produced orprepared by any technique, including conventional techniques known tothose skilled in the art.

For example, cement may be produced using a dry or wet process. In someembodiments, cement may be produced through controlled chemicalcombination of calcium, silicon, aluminum, iron and other ingredientsknown to those skilled in the art. The ingredients used to manufacturecement may include limestone, shells, and chalk or marl combined withshale, clay, slate, blast furnace slag, silica sand, and iron ore. Theseingredients may be heated at high temperatures to form a rock-likesubstance, which is then ground into fine powder to form cement.Concrete includes the addition of aggregates including sand, fly ash orground rock.

In a typical cement and/or concrete manufacturing process, finely groundraw materials, or a slurry of the raw materials mixed with water, may befed into the kiln at the top of the kiln. The lower end of the kiln isprovided with a flame, which may be produced by precisely controlledburning of powdered coal, oil, or other fuels or gases under forceddraft. As the materials move through the kiln, certain elements aredriven off in the form of gases, and the remaining elements unite toform a clinker, which is extracted or discharged from the kiln andcooled. The cooled clinker may ground and mixed with small amounts ofgypsum and limestone. In a dry process, the raw materials are groundwithout being mixed with water. In a wet process, the raw materials areground with water before being fed into the kiln. Heated limestonereleases carbon dioxide, Calcination of limestone, processing and fuelcombustion emit the greenhouse gas carbon dioxide in the manufacturingof cement and concrete.

Metallic or alloy structural materials may also be produced according toknown technics. As with cement or concrete, while metallic or alloystructural materials are widely evident through their pervasive use asin building, transportation, and commodity support and packaging, theirproduct carbon footprint substance ion has a high carbon footprintcontributing to global warming and climate change.

A carbon nanomaterial is provided at S14. The carbon nanomaterial is notproduced with conventional techniques such as CVD, arc discharge orlaser ablation that have high carbon footprints, but is produced by aprocess with a low carbon footprint of F_(c)≤10, such as F_(c)≤5,F_(c)≤3, F_(c)≤1, or F_(c)≤0. In some embodiments, F_(c)<0, where thecarbon nanomaterial is produced with net CO₂ consumption. In someembodiments, F_(c) is 0 to 1.

S16 combines the high carbon footprint substance S12 and low carbon footprint carbon nanomaterial S14 to produce a stronger composite requiringless of the original high carbon footprint substance.

For comparison purposes, FIG. 3 illustrates possible processes 20 withdifferent possible pathways 21, 31, 41, 51, 61, and 71 to formcomposites, and the challenges of existing material-carbon nanomaterialcomposite pathways 21, 31, 41 to lower carbon footprint materials, andthe removal of hurdles to greener carbon footprint substance that may beproduced according to an embodiment of the present disclosure, such asthrough pathways 51, 61 and 71.

In particular, at possible pathway 21, the high carbon footprintsubstance may be combined with a low carbon footprint carbonnanomaterial at 22. The pathway 21, however, inhibits, as indicated bythe cross (X) at 23, formation of a lower carbon footprint composite 24,due to the high carbon footprints of both the higher carbon footprintsubstance and the carbon nanomaterial. Thus, a person skilled in the artwould not have been motivated to take the pathway 21 to produce lowcarbon footprint composite materials 24.

At possible pathway 31, the carbon footprint substance may be combinedwith an expensive carbon nanomaterial at 32. However, the high costdis-incentivizes the skilled person to take pathway 31, and a skilledperson in the art would not have been motivated to take pathway 31, asindicted by the cross (X) at 33, to produce a lower carbon footprintcomposite material 34.

As illustrated at possible pathway 41, carbon nanomaterials produced bya conventional technique at 42 that tend to tangle and cannot behomogeneously dispersed in the high carbon footprint substance are notsuitable for producing a lower carbon footprint high carbon footprintsubstance 44, as indicated by the cross (X) at 43. It should beunderstood that uniform carbon nanomaterial dispersion can provideimproved properties of CNM-composites. However, CNMs produced in highvolumes by existing conventional techniques are generally agglomeratedor tangled, thus rendering them unsuitable for dispersion.

In comparison, in some embodiments of the present disclosure, one ormore of pathways 51, 61, 71 can be taken to reduce the production carbonfootprints.

According to some embodiments disclosed herein, an inexpensive and lowcarbon footprint composite material may be produced by taking thepathway 51. According to pathway 51, at 57 the carbon footprintsubstance can be combined with a low carbon footprint carbonnanomaterial produced at 52, to provide a stronger composite material at57 that decreases the amount of the high carbon footprint substance usedto achieve the same strength. Reducing the amount of the high carbonfootprint substance used would decrease the carbon dioxide emissions ofthe high carbon footprint substance production to lower the carbonfootprint of the composite material 57 relative to the original highcarbon footprint substance. Different factors or processing steps in theproduction of the carbon nanomaterial at 52 can contribute to thereduction in the production carbon footprint. For example, as indicatedat 53, a lower carbon footprint in the production of the carbonnanomaterial can be achieved producing the carbon nanomaterial using CO₂as the reactant. As indicated at 54, a more facile reactivity maycontribute to the reduction in the production carbon footprint. Asindicated at 55, a processing step that requires a lower energy and/orless carbon dioxide emitting energy may contribute to the reduction inthe production carbon footprint.

In pathway 61, the high carbon footprint substance is combined with alow cost carbon nanomaterial that is produced at 62 with a lowproduction cost, to form a composite 64 with a low carbon footprint. Thepathway 61 can provide a less expensive composite material 64 withincreased strength, which also decreases the amount of high carbonfootprint substance used to achieve the same strength and lowers thecarbon footprint of the composite material relative to the original highcarbon footprint substance.

In pathway 71, the high carbon footprint substance is combined with acarbon nanomaterial produced at 72 and tailored for a specificCNM-composite property enhancement to form a composite 74. Examples oftailored CNM may include boron doped CNM to improve CNM-compositeelectrical conductivity as well as strength, thick walled CNTs toimprove CNT-composite compressive strength, or long CNTs to improveCNT-composite flexural strength. The tailored CNMs combined with thehigh carbon footprint substance may be combined to form the desiredlower carbon footprint composite material at 74.

The carbon nanomaterial may be provided in the form of carbon nanofiberssuch as closed fibers or carbon nanotubes (CNT) of solid filled, solidnano filaments. The carbon nanotubes (CNT) may be single-walled CNT(SWCNT) or multi-walled CNT (MWCNT). The carbon nanofibers mayconveniently be untangled, i.e. having no entanglement or a low degreeof entanglement, for reasons to be discussed below.

In some embodiments the carbon nanomaterial, may be carbon nanofiberswith an average aspect ratio of 10 to 1000. The carbon nanofibers mayhave a thickness of 3 nm to 999 nm.

In some embodiments, the carbon nanomaterial may include carbonnano-onions, carbon nano-scaffold, carbon nano-platelet, or graphene.

In some embodiments, the carbon nanomaterial provided at S14 may includea combination of different forms, including those described above.

FIG. 4 illustrates an example system 100 for producing carbon nanotubesfrom molten carbonate by electrolysis. See also similar systemsdescribed in more details in WO 2017/066295 and WO 2016/138469.

The molten carbonate may be a lithium carbonate or lithiated carbonate.Molten carbonates, such as a lithium carbonate Li₂CO₃, which has amelting point of 723° C., or lower melting point carbonates such asLiBaCaCO₃, having a melting point of 620° C., when mixed with highlysoluble oxides, such Li₂O and BaO, sustain rapid absorption of CO₂ fromthe atmospheric exhaust CO₂. Suitable carbonates may include alkali andalkali earth carbonates. Alkali carbonates may include lithium, sodium,potassium, rubidium, cesium, or francium carbonates, or mixturesthereof. Alkali earth carbonates may include beryllium, magnesium,calcium, strontium, barium, or radium carbonates, or mixtures thereof.

Carbonate's higher concentration of active, reducible tetravalent carbonsites adjacent to the active reduction site at the cathode decreases theenergetics and facilitates charge transfer resulting in high rates ofcarbonate reduction at low electrolysis potentials. CO₂ can be bubbledinto the molten carbonate replenishing carbonate transformed to carbon,and during electrolysis, oxygen is evolved at the anode while a thicksolid carbon builds at the cathode. The resulting solid carbon may becarbon nanomaterials such as carbon nanofibers or carbon nanotubes.

A transition metal nucleating agent may be added during electrolysis ofthe molten carbonate. The transition metal creates nucleation sites thatallow the growth of the carbon nanomaterials. Example transition metalnucleating agents include nickel, iron, cobalt, copper, titanium,chromium, manganese, zirconium, molybdenum, silver, cadmium, vanadium,tin, ruthenium, or a mixture therein.

System 100 produces carbon nanomaterials from molten carbonate materialsand injected CO₂. System 100 includes a carbonate furnace 102, anelectrolysis chamber 104, and a collector 106. Although the furnace 102,the electrolysis chamber 104, and collector 106 are shown as separatecomponents in FIG. 2 , they can be provided and integrated in the samephysical structure. The electrolysis chamber 104 includes a chamber 110that holds molten carbonate produced by heating carbonate in the furnace102. An anode 112 and a cathode 114 are coupled to a power source 116.The anode 112 and the cathode 114 are inserted in the chamber 110. CO₂is injected into the molten carbonate from a CO₂ source 118. CO₂ gas isinjected into the molten carbonate to react with the oxide and renew,rather than consume, the carbonate, for the overall electrolysisreaction as CO₂ converted to O₂ at the anode 112 and carbonnanomaterials at the cathode 114.

Any CO₂ source may be used as CO₂ source 118. For example, environmentair may provide a CO₂ source. Emission gases from various plants orchemical reactors may provide CO₂ sources. For example, power generatingplants, steam generation facilities, or pyrolysis reactors may emit CO₂.CO₂ emitted from system 100 or in the production of the high carbonfootprint substance may also be used as a CO₂ source.

In some embodiments, during operation, the carbonate furnace 102 heats acarbonate, such as pure Li₂CO₃, to its melting point to produce moltencarbonate. A transition metal is added via a disperser that may be theanode to serve as a nucleation agent. The molten carbonate is subjectedto electrolysis by being inserted between the anode 112 and the cathode114 in the electrolysis chamber 104. The resulting reaction separatescarbon from the carbonate and leaves carbon product on the cathode 114from the nucleation sites. The resulting carbon product is collected inthe collector 106 while oxygen is produced on the anode 112.

In some embodiments, the molten carbonate may be a lithium carbonate,Li₂CO₃, and the metal oxide may be a lithium oxide, Li₂O. The carbonnanomaterial, such as carbon nanotubes, may be produced in an reactionrepresented by:Li₂CO₃→C_(CNM)+O₂+Li₂O  (1)

Atmospheric CO₂ rapidly and exothermically dissolves in the electrolyte,chemically reacting with lithium oxide to renew and reform Li₂CO₃,CO₂+Li₂O→Li₂CO₃  (2)

Electrolysis, via equation (1), releases Li₂O to permit continuedabsorption of CO₂, via equation (2). Taking the net reactions ofequations (1) and (2), CO₂ is split by electrolysis to form carbonnanomaterials and oxygen, under the net reaction:CO₂→C_(CNM)+O₂  (3)

As indicated by equation (3), CO₂ is split and oxygen is released whilesolid carbon is formed at the cathode 114.

In other embodiments, different carbonates, or carbonate mixes, may beused to replace the lithium carbonate. In such cases, equations (1) and(2) may be correspondingly modified but equation (3) can remain thesame, as can be understood by those skilled in the art.

Transition metals, such as Ni or Cr, may be added to nucleate CNMformation. The added transition metal may be less than 0.1 wt % of theproduct. The transition metal or nucleate agent can be added to theelectrolyte or to the cathode 114, or may be added by leaching from theanode 112.

The furnace and electrolysis chamber in the system 100 may be powered byany power source or a combination power sources, including electricalpower sources and solar power sources. Heating is provided by theexothermic reaction of carbon dioxide absorption and conversion tocarbonate.

The produced carbon nanomaterials may have nanofiber such as nanotubestructures. For example, carbon nanofibers may be produced at thecathode 114 when the anode 112 is a nickel anode and electrolysis isconducted in a corrosion-free lower temperature of 630° C. with a Li₁₋₆Ba_(0.3) Ca_(0.1) CO₃ electrolyte.

The produced carbon nanomaterials may also have amorphous and plateletstructures. For example, when the anode 112 is a platinum anode (anddoes not contain nickel or nickel coating) and a Li₃CO₂ carbonate isheated to a temperature of about 730° C., carbon platelets may beformed, which have partially formed multi-layered graphene/graphite andmay contain greater than 99 wt % carbon.

As described in the above cited literature, the type and characteristicsof the carbon nanomaterial produced using system 100 can depend on, andthus be controlled by adjusting, the electrical current level, thecomposition of the electrolyte, the reaction temperature, the viscosityof the electrolyte, the amount of transition material present, and thecathode and anode materials.

For example, the anode 112 may include platinum, iridium, and nickel. Inlithium carbonate electrolytes, nickel corrosion at the anode 112 isslow and is a function of anode current density, electrolysis time,temperature, viscosity, and lithium oxide concentration.

Conveniently, producing carbon nanofibers from molten carbonates and CO₂by electrolysis can form homogenous carbon nanofibers, which can beconveniently dispersed homogenously into the structural material as willbe further described. In particular, it has been shown in the literaturethat the nickel presence at anode 112 may be controlled so that thenickel can act as a nucleating agent to facilitate formation ofhomogenous carbon nanofibers.

It has also been shown that carbon nanofibers produced by electrolysisin pure molten Li₂CO₃, without adding Li₂O, can be consistentlyuntangled, uniform, and long. The resulting carbon nanofibers can beuniform nanotubes having a width of 0.3 to 1 μm and a length of 20 to200 μm, with an aspect ratio of about 20 to about 600.

Additives may be added to the molten electrolyte to control theproperties of the produced carbon nanomaterials. Some additives, such asnickel, can act not only as nucleating sites, but also as filling agentsin the formed hollow nanotubes. Additives other than oxides ortransition metal salts can also act as carbon nanomaterial filling orcoating agents, or be used to affect the viscosity of the electrolytes.For example, both inorganic aluminate and silicate salts are highlysoluble in molten lithium carbonate. High concentrations of eitherinorganic aluminate or silicate salts can increase the viscosity of theelectrolyte.

As previously described, a high applied electrolysis voltage, generallyin excess of ˜3V during the electrolysis, can yield lithium metal,aluminum metal or silicon with, on or in the carbon nanomaterials.

Different types of nanomaterials may be generated by controlling theelectrolysis process, conditions, and the materials present in theelectrolyte and at the anodes. For example, as described in theliterature, straight and untangled carbon nanotubes can be produced frommolten carbonate electrolyte if no Li₂O is added during electrolysis. Incontrast, tangled carbon nanotubes may be formed if Li₂O is added to themolten carbonate electrolyte during production. The diffusion conditionsduring electrolytic splitting of CO₂ in molten lithium carbonate can beadjusted to control whether the formed carbon nanofibers are solidfibers (filled nanofibers) or hollow carbon nanotubes. The oxide andtransition metal concentrations can be adjusted to further control theformation of tangled or straight (untangled) fibers. For the purpose ofconvenient homogeneous dispersion of the carbon nanomaterials in thestructural material, homogeneous untangled nanofibers with more uniformsizes are more desirable, and can be produced using system 100.

The power source for system 100 may be an electric source such as asource of electrical power generated by a coal, natural gas, solar,wind, hydrothermal, or nuclear power plant. As an alternative toconventionally generated electrical sources, the carbon nanomaterial maybe produced using electric current generated by a solar cell.

Alternative CO₂ sources may be used, which may include oxides of a ¹²C,¹³C or ¹⁴C isotope of the carbon, or mixture thereof. For example, ¹²CO₂may be suitable for forming hollow carbon nanotubes under certainconditions. Under similar conditions, adding heavier ¹³CO₂ to the moltencarbonate can facilitate formation of solid core carbon nanofibers.

Atmospheric CO₂ has been used to form multi-walled carbon nanotubeaccording to a process described herein.

By controlling the electrolysis conditions, the produced product mayalternatively include amorphous graphites or graphenes.

In some embodiments, the system 100 in FIG. 2 may be used to transformCO₂ gas dissolved in the molten carbonate electrolyte by electrolysis ata nickel anode and at a galvanized steel cathode. At the anode 112 theproduct is O₂ and at the cathode 114 the product contains uniform carbonnanofibers, which may be carbon nanotubes. Carbon nanotubes may befavored if the electrolysis is performed at lower current densities ofthe molten carbonate without added Li₂O electrolytes.

Amorphous carbon may be produced at a steel cathode without the use of atransition metal anode. Use of a zinc coated (galvanized) steel cathodeand a non-transition metal anode in electrolysis can produce sphericalcarbon nanomaterials. Use of a zinc coated (galvanized) steel cathodeand a non-transition metal anode in electrolysis but with high ironcontent from iron oxide dissolved in the electrolyte can produceamorphous carbon as well as a wide variety of carbon nanostructures onthe cathode.

Zinc metal on the cathode can lower the energy to form carbon and helpinitiate the carbon nanotube or carbon nanofiber formation process. Thepresence of the zinc metal can act as a beneficial aid as it isenergetically sufficient to activate both (i) the spontaneous formationof solid carbon from carbonate and (ii) the spontaneous formation ofmetal catalyst nuclei that aid initiation of the controlled structuregrowth of carbon nanomaterials at the nucleation site. Zinc therebyfacilitates subsequent high yield carbon nanomaterial growth from CO₂dissolved in molten carbonate.

The cathode 114 and the anode 112 may have any number of shapes. Forexample, the anode 112 and cathode 114 may be a coiled wire, a screen, aporous material, a conductive plate, or a flat or folded shim. They canalso form inner sides of the electrolysis chamber 104.

It is also noted that in some embodiments, when a relatively highcurrent density is applied in electrolysis, amorphous carbon and avariety of carbon nanostructures are more likely produced. When aninitial low current density and then a high current density is appliedin combination with Li₂O in the molten carbonate electrolyte, high yielduniform but twisted carbon nanofibers are likely produced at the cathode114. When an initial low current density and then a high current densityis applied in combination a molten carbonate electrolyte without Li₂O,high yield uniform straight carbon nanofibers or carbon nanotubes areproduced at the cathode 114.

In brief recap, during CO₂ electrolysis for producing carbonnanomaterials, the transition metal deposition can control nucleationand morphology of the carbon nanostructure. Diffusion can control theformation of either carbon nanotubes as grown from natural abundance CO₂or carbon nanofibers from ¹³C isotope morphologies. The electrolyticoxide controls the formation of tangled nanotubes from a high Li₂Omolten carbonate electrolyte or straight nanotubes when the moltencarbonate electrolyte has no added Li₂O.

A transition metal such as nickel may be added on the anode 112, whichcan be dissolved from the anode 112 to migrate through the electrolyteonto the cathode 114. The added transition metal can function as anucleating agent, which may be selected from nickel, iron, cobalt,copper, titanium, chromium, manganese, zirconium, molybdenum, silver,cadmium, tin, ruthenium, or a mixture thereof. The transition metal mayalso be introduced as a dissolved transition metal salt to theelectrolyte directly to migrate onto the cathode 114. It is alsopossible to add the transition metal nucleating agent directly onto thecathode 114.

Low carbon footprint CNTs were previously scarce with technicalchallenges to scale-up, and the possibility mass production wasunproven. Prior molten carbonate produced CNMs provided technicalchallenges to scale-up, such as scale-up to industrial dimensionelectrodes, high current interconnects compatible with high temperaturemolten carbonates, and management of the CO₂ gas reactant in industrialconditions. FIG. 5 comprises photographs of building the 2 tonne CO₂daily conversion industrial C2CNT plant. The technical challenges of gasmanagement plant is overcome with heat exchange between the incidentflue gas as the CO₂ source and the exhaust gas freed of CO₂. Theindustrial dimension electrodes and high temperature interconnects areoperational. The system converts flue gas from the adjacent 860 MWShepard Energy Centre, Calgary, Calif. natural gas power plant.

Due to the expense, energy intensity and complexity of the synthesisindustrial CNTs, generally produced by variants of the chemical vapordeposition process, currently cost to produce in the range of $100K($85-$450K) per ton range and do not use CO₂ as a reactant. This highcost de-incentivizes their use as an additive to reduce the CO₂emissions of structural materials and leads prior art way from anyconceptualization of the current invention. All components of the moltencarbonate electrolytic transformation of CO₂ to graphene areinexpensive. The transformation bears many similarities to theproduction of aluminum, and may be compared to the established costs ofthis latter, mature industry. In the 19^(th) century aluminum was moreexpensive than gold with little market. However, via a change ofchemical technology today aluminum is inexpensive with a mass market.Both processes entail the straightforward, high current density, moltenelectrolytic electrochemical reduction of an oxide, and do not use nobleor exotic materials. CO₂ electrolysis in molten carbonate production ofcarbon nanomaterials readily scales upward linearly with the area of theelectrolysis electrodes, facilitating the analogous larger scalesynthesis of graphene. The aluminum electrolysis uses and consumes acarbon anode that emits carbon dioxide, whereas the molten carbonatecarbon nanomaterial electrolysis anode is not consumed and emits oxygen.52% of the $1,880 per tonne cost of Al production consists of bauxiteand carbon; whereas this molten carbonate electrolysis does not consumecarbon as a reactant and uses a no-cost oxide as the reactant to bereduced (CO₂, rather than mined bauxite). Molten carbonate CO₂electrolysis costs, such as kilns, electrodes and electrolyte, aresimilar, but less expensive than the industrial production of aluminum.

In addition to a higher carbon footprint, the aluminum processnecessitates a larger physical footprint. Aluminum production uses thehigher density of liquid aluminum compared to the density of thefluoride electrolyte to collect the aluminum product from a horizontalelectrode; whereas the nanocarbon product resides on the cathode, whichtherefore may be stacked vertically in a low physical footprintconfiguration. The carbon nanomaterial molten carbonate electrolysis,process operates under somewhat milder conditions at ˜700 to 800° C. ina less exotic, molten carbonate electrolyte at similar rates of output,but at 0.8 V to <2 V potential compared to an electrolysis potential ofover 4 V for aluminum.

Hence, $1,000 is a reasonable upper bound estimation to industrialcarbon graphene production by carbon dioxide electrolysis, excludinganode and exfoliation costs to be determined, in molten carbonates. Thiscost is significantly lower than the current price of graphene, and mayprovide a significant incentive to use the greenhouse gas carbon dioxideas a reactant to produce carbon graphene. This can provide a useful pathforward to help break the anthropogenic carbon cycle to mitigate climatechange.

Different CO₂ sources may be used for the above described process ofproduction of carbon nanomaterials. For example, the CO₂ source may beair or pressurized CO₂. The CO₂ source may be concentrated CO₂, such asthat found in a smokestack or flue, including chimneys, and industrialstacks such as in the iron and steel, aluminum, cement, ammonia consumerand building material, and transportation industries.

Another source of CO₂ may be from hot CO₂ generated during fuelcombustion in a fossil fuel electric power plant. In such a system,electricity and carbon nanomaterials may be produced without CO₂emission. A portion of the fossil fuel electric power plant outputspower for the electrolysis process. The O₂ electrolysis product may bereinjected back into the fossil fuel electrical power plant.

Alternatively, a second source of non-CO₂ emitting electricity, such asrenewable or nuclear powered electricity, may be employed to power theelectrolysis process, and the O₂ electrolysis product may be injectedback into the fossil fuel electrical power plant.

Some embodiments of the disclosure thus relate to a method of forminglow carbon foot print structural materials. The method includesproviding a structural material, providing a reinforcement materialcomprising a low carbon footprint carbon nanomaterial (CNM) formed witha carbon-footprint of less than 10, and forming a composite comprisingthe structural material and 0.001 wt % to 25 wt % of the carbonnanomaterial. The carbon nanomaterial is dispersed homogeneously in thecomposite. In some embodiments, the carbon nanomaterial is formed from amolten carbonate by electrolysis, along with oxygen and dissolved metaloxide, as will be further described below.

In some embodiments, a power plant can provide a CO₂ source from theflue stacks that is fed into an electrolyzer. The electrolyzer maycontain a molten electrolyte such as lithium carbonate along with ametal cathode that can be copper, stainless steel, or a Monel cathode.As described above, transition metal nucleated electrolysis produces acarbon nanomaterial product, along with oxygen. Compared to conventionalmethods for producing carbon nanomaterials, the method described abovehas a significantly lower overall output of greenhouse gases. The carbonnanomaterial can then be combined with a structural material to create acarbon nanomaterial composite.

The hot oxygen product of the electrolysis reaction is useful in a rangeof processes if recovered. The recovered oxygen can then be used as afeedstock for the manufacture of a range of oxygen containing products.For example, a variety of industrial chemicals and monomers such asTiO₂, ethylene and propylene oxides, acetaldehyde, vinyl chloride oracetate and caprolactam can be prepared. Additionally, the hot oxygensource can be used as an alternative to air in combustion, resulting inless fuel consumed or generating a higher combustion temperature.

The carbon nanomaterials are synthesized from electrolysis of CO₂ andmay include carbon nanotubes, carbon nanofibers, carbon nano-onions,carbon nano-platelets, carbon nano-scaffolds, or graphene. In each casethe products may be synthesized to a high coulombic efficiency of over95% and in some cases the purity may be over 95%.

When carbon nanofibers are used, they may have an aspect ratio of 10 to1000, and an average thickness of 3 to 999 nm. Untangled CNTs with ahigh aspect ratio may be readily dispersed in water with sonication toform homogeneous dispersion.

The electrolysis conditions can be controlled to produce CNTS ofselected uniform thickness, having twisted or straight longitudinalshape; or to produce thick straight CNTs.

In some embodiments, tangled 5-8 μm long CNTs can be grown on a coppercathode nucleated with Ni powder added to the electrolyte to providenucleation points for CNT growth. Electrolysis may be performed overdifferent time lengths, such as 15, 30 or 90 minutes, to yield carbonnanofibers with different thickness, such as thin (˜20 nm), medium (˜47nm), or thick (˜116 nm) walled CNTs. Multi-walled CNTs may exhibit thedistinctive graphene layered characteristic 0.335 nm separation betweenconcentric cylindrical walls. By pasting nickel powder directly on thecopper cathode prior to electrolysis, straight 5-10 μm long CNTs can beformed at the nickel nucleation points.

In some embodiments, when an extended charge, Monel cathode, and nickeland chromium induced nucleation electrolysis is instead applied, verylong CNTs with a length of 200-2000 μm can be produced.

In some embodiments, after 5 hours synthesis using a brass cathode undervarious controlled conditions, a carbon nanotube product includingbunched, straight or thicker CNTs can be produced.

In some embodiments, cement and carbon nanotubes may be co-produced in aplant with a negative carbon footprint (F_(c)<0), for example, asdisclosed in Licht, “Go-production of cement and carbon nanotubes with acarbon negative footprint,” J. CO ₂ Utilization, 2017, vol. 18, pp.378-389.

A process described herein can be scaled to produce large quantities ofcommercially valuable products and by-products.

Returning to FIG. 1 , at S106 the structural material and the carbonnanomaterial are mixed or combined to form a composite.

A wide variety of methods can be utilised to incorporate the abovedescribed CNMs into the desired structural material. Having a homogenousdispersion of the CNM within the structural material can provideimproved mechanical properties in the resulting composite material.

As used herein, a homogeneous dispersion of the carbon nanomaterial inthe composite refers to substantially uniform distribution of the carbonnanomaterial, such as carbon nanofibers, throughout the composite, sothat the composite has substantially uniform mechanical properties indifferent regions of the composite. It is not necessary for thenanomaterial to be dispersed at molecular levels, or at individual fiberlevels when nanofibers are dispersed. Limited aggregation orentanglement of the fibers within small domains, such as domains withdomain sizes less than about 1,000 μm may be tolerated in someapplications. However, larger domains of concentrated carbonnanomaterials unevenly distributed in the composite can cause materialdefects or weakness, or reduce the efficient utilization of thereinforcement materials.

In some embodiments the structural material is cement. In order toincorporate the CNM into the cement, a dispersion of the CNM in anaqueous liquid such as water can be formed by addition of the CNM towater, followed by mixing using bath sonication to uniformly and evenlydisperse the CNM in the liquid mixture. In some embodiments, asurfactant may be added to prevent agglomeration of the CNM. The CNMdispersion may be then added to dry cement powder, along with additionalwater if required. Mechanical mixing may be used to fully disperse theCNM in the aqueous cement mixture, so the CNM is homogeneously dispersedin the admixture and the resulting composite will contain homogeneouslydispersed CNM.

In some embodiments, homogeneous dispersion of the CNM in the admixturemay be facilitated by sonication, adding a surfactant, or stirring, orany combination thereof. Conveniently, sonication does not require asignificant carbon footprint.

In some embodiments, the above described processes can be used to formconcrete, mortar, or grout that contains cement and homogeneouslydispersed CNM.

The addition of 0.048 wt % of CNT can increase cement, concrete, mortaror grout tensile strength by 45%. Hence, for a simple (one dimensionalapplied force) usage case, such as a thinner CNT-cement composite tobear the same load, 1 tonne of CNT can replace 938 tonne of aluminum.Using a CNT-cement composite containing 1 tonne of CNT to replace cementcan reduce 844 tonnes of emitted CO₂ during cement, or in the samemanner, concrete, mortar or grout, production. This process of reducingthe CO₂ emission in the production of cement through the addition of lowcost or low F_(C) carbon nanotubes is illustrated in FIG. 12(A). Thefigure shows the massive carbon dioxide avoidance by addition of carbonnanotubes synthesized from CO₂ to CNT-composites with CNT-cement. B:Carbon mitigation with CNT-Al. The latter (B) includes a cascade effectdue to virgin Al's large carbon footprint triggering larger CO₂ emissionelimination.

In some embodiments, the structural material may be aluminum. A heatingapparatus such as an air induction heater may be used to heat solidaluminum until molten after which a CNM may be added. The strongconvective currents ensures the CNM is well dispersed within the moltenaluminum which may then subsequently be cast into ingots or processedinto a final product. Oxygen may be excluded from this method to preventoxidation of the CNM due to the high temperatures. Alternatively, asimilar composite may ultimately be formed by addition of a CNM toaluminum powder. Mixing of the two materials may be affected by aprocess such as ball milling, followed by hot extrusion.

The addition of 0.1 wt % of CNT can increase aluminum tensile strengthby 37%. Hence, for a simple (one dimensional applied force) usage case,such as a thinner CNT-Al composite foil to bear the same load, 1 tonneof CNT can replace 370 tonne of aluminum. Using a CNT-Al compositecontaining 1 tonne of CNT to replace virgin aluminum can reduce 4,403tonnes of emitted CO₂ during aluminum production. This process ofreducing the CO₂ emission in the production of aluminum through theaddition of low cost or low FC carbon nanotubes is illustrated in FIG.12(B). The figure shows the massive carbon dioxide avoidance by additionof carbon nanotubes synthesized from CO₂ to CNT-composites withCNT-aluminum and includes a cascade effect due to virgin Al's largecarbon footprint triggering larger CO₂ emission elimination.

In some embodiments, a low carbon footprint composite may be preparedusing magnesium and CNM. It is expected that CNM agglomeration woulddecrease CNM-metal interaction, thus prevent formation of effectivemagnesium-CNM composites. This problem may be addressed by coating theCNMs with nickel, to provide an effective Mg₂Ni interface between theCNM and magnesium. By adding 0.3 wt % of Ni-coated CNTs, theCNT-magnesium composite can exhibit an increased tensile strength, suchas by 39% as compared to pure magnesium. Replacing magnesium with aCNT-Mg composite of equivalent strength can reduce CO₂ emission by 1,820tonnes per tonne of CNT.

Production of a low carbon footprint composite using metals with highermelting points such as titanium, copper and steel can be morechallenging due to difficulties in achieving uniform dispersion of theCNM. When the metal used is titanium, a premix of elemental titaniumpowders can be formed, and then subjected to spark plasma sintering.

In some embodiments the metal for forming the composite may be copper. Asuspension of CNM in a solvent may be formed, and copper powder may beadded to the CNM suspension to form a mixture. The mixture may besubjected to calcination and reduction to produce copper-CNT compositepowder, which has CNMs homogeneously dispersed within the powder. Insome embodiments, the mixture may be sintered, such as by spark plasmasintering or microwave sintering, to form the composite material.

With homogeneous dispersion of 1 wt % CNTs into copper in the resultingCNT-Cu composite, a 207% strength increase in the CNT-Cu composite hasbeen observed. Such a composite can proportionally replace 67 tonnes ofcopper by 1 tonne of CNT, and still provide the same mechanical strengthto copper. The carbon footprint of copper production varies widely byregion, but globally has a combined average of approximately 5 tonne CO₂per tonne Cu. By replacing copper production with the production ofequivalent CNT-Cu composite, emission of CO₂ during production can besubstantially reduced. For example, emission of 337 tonnes of CO₂ can beavoided if 67 tonnes of copper is replaced with one tonne of CNT andeach tonne of copper production emits 5 tonnes of CO₂.

In some embodiments, the structural material may be stainless steel. CNMmay be added in solid form to the steel powder and the resulting mixtureis placed in a ball mill to grind and blend the ingredients together (byball milling), followed by spark plasma sintering to form the compositematerial. The massive global annual production of stainless steelcoupled with a high carbon footprint, F_(c)=6.15, which includes 5.3tonnes of CO₂ emission for generating the energy required to produce onetonne of steel.

A CNT-stainless steel composite containing 0.75 wt % CNT can exhibit 37%higher strength. Thus, it is expected that using CNT-stainless steelcomposite to replace stainless steel can reduce CO₂ emission by 302tonnes CO₂ per tonne of CNT.

The net energy required by the transformation of CO₂ to CNTs is 2.0 MWhper tonne CO₂ reacted to CNT (1.6 MWh at 0.8V).

The reduction in CO₂ emission associated with using different compositesof CNM with cement, aluminum, magnesium, titanium, or stainless steel,and the corresponding improvement in mechanical strength are summarizedin Table I.

In Table I, the last column lists the net energy consumed bytransformation of CO₂ to CNTs by electrolysis in molten carbonate.

TABLE I Reduction in Reduction in Energy required wt % Change instructural material CO₂ emission per tonne CO₂ CNT Strength Strength(ton) F_(c) (ton) (kWh) cement 0.048% tensile 45% 938 0.9 840 2.45aluminum 0.10% tensile 37% 370 11.9 4400 0.47 magnesium 0.30% tensile39% 130 14 1820 1.14 titanium 0.3% yield 102%  339 8.1 2750 0.75stainless steel 0.75% tensile 37% 49 6.15 302 6.85 copper 1.0% tensile207%  207 5 337 1.14

In some embodiments, the structural material may a polymer, such as apolymer plastic. A CNM may be added to a molten plastic, followed bymechanical mixing to disperse the CNM. The composite may then be formedinto a final product via a process such as injection molding, blowmolding or extrusion.

In some embodiments, the structural material may be a wood material. Inan example, CNMs may be added in solid form during the production ofmedium density fibreboard (MDF). Addition of solid CNMs to wood fibresprior to addition of a urea-formaldehyde resin, followed by pressinginto sheets yields a composite material.

In some embodiments, the structural material may be a cardboard. SolidCNMs may be added to a slurry of wood pulp fibres formed from pinechips. This slurry can then be pumped into a paper making machine toform kraft paper. The kraft paper is corrugated into the CNM cardboardcomposite material.

In some embodiments, the structural material may be a laminate ordrywall. During the production of a gypsum plaster layer, CNMs may beadded to a mixture of gypsum plaster, fibre, plastizer, foaming agentand chelator that is sandwiched between two sheets of heavy paper orfibre glass. The CNMs may be added to the wet mixture either in solidform or as a suspension in a solvent such as water to provide additionalstrength to the drywall. A laminate is formed from layers to form a flatmaterial. The laminate layers may be formed from CNM-composite withresin, plastic, wood fibres, papers or simply hard layers of CNMcontaining electrolyte as illustrated in FIG. 9 . The exhibits the easeat which as-grown films that are removed by simple peeling from thecathode. The film is grown by an 18 hour electrolysis at 0.1 A cm⁻² in770° C. molten Li₂CO₃ on an 12.5 cm×20 cm electrode. The Inconel anodeand 304 steel electrolysis case are not affected by repeat electrolysis.The film thickness is directly proportional to the electrolysis timeallowing films in this objective of 0.0004″ (or less) to be studied. Thefilm is a mirror reflection of the cathode surface. In this case, thegold colored Muntz Brass is used to highlight that the cathode materialis not transferred to the grown film, that the cathode is ready forre-use (subsequent to film peel), and that the removed film mirrors theslightly deformed cathode surface. Muntz Brass has the lowest meltingpoint, 899° C., of the cathodes studied. The deformation which occursduring electrolysis at 770° C. is controlled by a steel brace on theelectrode side hidden from the anode, and the minor deformationexaggerates that the flatness of the peeled film mirrors the cathodesurface.

In some embodiments the CNM may be added in solid form to the cementpowder and the resulting mixture is placed in a ball mill to grind andblend the ingredients together prior to addition of water.

It should be noted that homogeneous dispersion of CNM in the compositecan provide a stronger composite. Thus, measures will need to be takento avoid non-homogeneous distribution, such as local concentration, ofthe CNM in the composite. For example, tangled CNTs tend to agglomerateand are not readily miscible in aqueous mixtures. Thus, untangled CNTsproduced from molten carbonate by electrolysis are particularly suitablein an embodiment of the present disclosure. In the production of theCNTs, the electrolysis conditions should be controlled and can bemodified to provide precise control over the carbon nanotube productmorphology.

In different embodiments, a CNM product can be formed in either pureLi2CO3 or mixed binary or ternary lithiated, or lithium-free moltencarbonates at 750° C.

It is noted that mixtures of alkai (lithium, sodium, or potassium)carbonates are less viscous than a pure molten carbonate salt.

Anodic corrosion during electrolysis may be avoided ore reduced byexclusion of potassium carbonate from the electrolyte.

It has been shown that addition of merely 0.048 wt % (C) CNT to cementcan form a composite having increased tensile strength (S), such as by45%, as compared to the tensile strength of pure cement. Therefore, insome cases, a thinner layer of the composite comprising cement and CNTcan provide the same strength as a thicker layer of pure cement. As aresult, cement usage may be reduced. In other cases, CNT may be used asa reinforcement material in concrete to replace other reinforcementmaterials that have high carbon footprints, such as steel. In suchcases, while cement usage may not be reduced, the overall carbonfootprint of the concrete is still reduced.

In a simple usage case, such as a thinner floor to bear the same load, a1/1.45 as thick, but 45% stronger, CNT-cement composite can have thesame strength as cement without CNT. That is, a composite of 1 tonne-CNT(0.048 wt %) in 2082 tonnes of cement has the same strength as 3021tonne of cement. Thus, using a CNT-cement composite containing one tonneCNT can reduce the needed cement by 938 tonne. As a result, a muchsmaller carbon footprint is required by replacing pure cement with theCNT-cement composite.

It can now be appreciated that a carbon nanomaterial produced with acarbon-footprint of less than 10 unit weight of carbon dioxide (CO₂)emission during production of 1 unit weight of the carbon nanomaterialmay be used for reinforcing a structural material. In some embodiments,the carbon nanomaterial may be produced from a molten carbonate byelectrolysis. The composite may be a composite disclosed herein.

In some embodiments, a carbon nanomaterial may be used in a compositecomprising a structural material to reinforce the structural material,wherein the carbon nanomaterial is produced with a carbon-footprint ofless than 10 unit weight of carbon dioxide (CO₂) emission duringproduction of 1 unit weight of the carbon nanomaterial. In someembodiments, the carbon nanomaterial may be produced from a moltencarbonate by electrolysis. The composite may be a composite disclosedherein.

In some embodiments, a carbon nanomaterial produced with a lowcarbon-footprint is used in a composite comprising a structural materialand the carbon nanomaterial, for reducing overall emission of carbondioxide (CO₂) during the manufacture of the composite, wherein the lowcarbon-footprint is a carbon-footprint of less than 10 unit weight ofCO₂ emission during production of 1 unit weight of the carbonnanomaterial. In some embodiments, the carbon nanomaterial may beproduced from a molten carbonate by electrolysis. The composite may be acomposite disclosed herein.

Assuming “W” represents the weight of a composite of the structuralmaterial and CNM, “N” represents the pure structural material withoutadded CNM, “C” represents the CNT weight concentration in the composite,and “S” represents the strength increase in percentage, the weight ofthe composite containing 1 unit weight of CNT is:W=100%/C  (4)

N can be determined by,N=W×(100%+S)/100%,  (5)

The weight reduction of the structural material in the composite fromthe pure structural material (N−W) isN−W=W(100%+S)/100%−W=W×(S/100%)  (6)

EXAMPLES Example I

It was demonstrated by testing that untangled CNTs with a high aspectratio were readily dispersed in water by sonication without the use of asurfactant. The water dispersed CNTs were admixed with Portland cementto form a CNT-cement composite. See FIGS. 3A, 3B and 3C.

In this example, the sample CNTs shown in FIG. 3A were formed byelectrolysis in a low viscosity binary lithium-sodium carbonateelectrolyte. Untangled CNTs were synthesized at 740° C. in the moltenelectrolyte containing 73 wt % Li2CO3, 17 wt % Na2CO3, and 10 wt % LiBO2by electrolysis using a brass cathode and an Inconel cathode, with asystem as illustrated in FIG. 2 . It was also observed that adding ametaborate salt to the electrolyte improved the aspect ratio of theCNTs.

The scanning electron microscope (SEM) image of the CNT product shown inFIG. 3A contained about 90 wt % CNTs. The electrolysis process occurredat 97.5% coulombic efficiency, determined with equation (3) comparingthe moles of CNT product to the integrated electrolysis current.

The CNTs were dispersed in water and the resulting aqueous mixture wassonicated. As can be seen in FIG. 3B, sonication caused homogeneousdispersion of the CNTs in water. It was also observed that, withoutsonication, CNTs agglomerated in water and the CNTs were nothomogeneously dispersed in water.

Upon mixing the aqueous suspension of homogeneously dispersed CNTs withPortland cement, the resulting admixture was readily cast intoCNT-cement composites, as shown in FIG. 3C. Less than 0.8 wt %, such as0.048 wt %, of the produced CNTs was added to Portland cement to formthe CNT-cement composite.

It was observed that less than 0.75 unit weight of the composite couldprovide the same mechanical strength as 1 unit weight of the purecement, a reduction in mass by at least 25%.

Example II

In this example, sample materials were produced with the followingobjectives to provide strong CNT-cement composites: (i) unbundling thecarbon nanotubes produced to allow an even and homogeneous dispersion ofthe CNTs throughout the cement and (ii) producing longer CNTs to bridgecement grains in the composite.

A CNT synthesis technique referred to as C2CNT technique was used toproduce the CNTs. The C2CNT technique involved electrolytic carbonateCO₂ splitting technology and was shown to provide CNT morphologycontrol, and could produce long, uniform, untangled CNTs to avoid thebundling of CNTs during mixing with water and cement, and allowedconvenient dispersion of the CNTs in a water mixture.

Oxygen was excluded during the addition of the CNMs to the structuralmaterial to avoid any oxidation of the CNMs being added.

Example II(1)

CNM-cement composites were made by facile dispersion of CNMs in water,by sonication or by surfactant addition, and then addition to cementpowder, with or without aggregates to form CNM-cement composites andCNM-concrete composites.

Example II(2)

CNM-aluminum composites were made by adding CNMs to melted aluminum(Melting point 660° C.). The CNMs were readily dispersed in the meltedaluminum. Inductive heating was used to melt the aluminum.

Example II(3)

CNTs made by the C2CNT technique were found to have a negative carbonfootprint of at least 800 tonnes CO₂ avoided per tonne of CNT produced(see Table I).

It was observed that including 0.048 wt % CNT produced by the C2CNTtechnique in the CNT-cement composite resulted in an increase in tensile(Young's modulus) strength by 60.8% (after curing for 26 days) and anincrease in compressive strength by 80.4% (after curing for 20 days), ascompared to the pure cement without the CNTs.

These strength increases were higher than those listed in Table I andhigher than the strength increases reported in the literature known tothe inventors. The increased strength was expected to be due to thehigher uniformity and less bundled nature of the carbon nanotubesprepared by the C2CNT technique.

Without being limited to any particular theory, it was expected that toform stronger CNM-cement composites, not only the CNM's own strengthsshould be high, so as to provide tensile, compressive and flexuralstrength enhancements, but also the added CNM should be able to bridgegrains of the cement. These bridges were expected to provide a matrixthat propagates the strength throughout the bulk composite.

It was observed that the C2CNT technique could control the uniformlength and diameter of the produced CNTs. CNTs with uniform thicknessand lengths were produced with the C2CNT technique, which included CNTshaving a diameter of 200 nm and a length of 80 μm. These CNTs were usedto form sample CNT-cement composites, which exhibited the above notedimproved strength.

To form the composites, the CNTs were dispersed in water andultra-sonicated prior to mixing with Portland cement powder. Beforesonication, the majority of the CNTs sank to the bottom of the mixingvessel, while some floated on the top of the water. Subsequent to 90minutes of sonication an evenly colored brown/black solution wasobtained (see representative photo shown in FIG. 3B). The CNTs evenlydispersed in water were mixed with Portland cement powder. The admixturewas set in various shaped casts and cured prior to testing.

Cylinder and figure “8” casts were used for the compression and tensilestrength tests. Representative test strength results are presented inTable I.

Example III

The C2CNT technology was also modified and used to produce other carbonnanomaterials, including graphene, nano-onions, nano-platelets,nano-scaffolds and helical carbon nanotubes. It was observed that eachof these CNMs exhibited unusual and valuable physical chemicalproperties such as lubrication (nano-onions), batteries (graphene) andenvironmental sorbents (nano carbon aerogels) prior to addition tostructure materials, and special properties including improvedelectrical conductivity and sensing ability for CNM-structural materialcomposites.

It is expected that these materials could provide improved structuralmaterials.

In each case the product was synthesized to a high coloumbic efficiencyof over 95%, and in most cases the product had a purity over 95%.

It was observed that a key measurable characteristic correlated tostrength was a low defect ratio as measured by the ratio of the ordered(G peak, reflecting the cylindrical planar sp² bonding amongst carbons)as compared to disorder (D peak, reflecting the out of plane sp³tetrahedral bonding amongst carbons) in the Raman spectra. Samplemulti-walled carbon nanotubes produced by the C2CNT technique exhibiteda high (strength) G:D ratio in the Raman spectra as shown in FIG. 6 .

Similar Raman spectra of sample carbon nano-onions produced the C2CNTtechnique is shown in FIG. 6 . Raman spectra of sample carbonnano-platelets produced the C2CNT technique is shown in FIG. 8 top andof sample graphene produced the C2CNT technique in FIG. 8 bottom. Thepresence of the D′-band is indicative of the layered single and multiple(platelet) graphene layers, and the left shift of the 2-D band indicatesthe thin graphene layer.

FIG. 9 presents SEM of carbon nano-scaffolds, which are grown at 670° C.in a 50% Na₂CO₃ and 50% Li₂CO₃ electrolyte at a current density of 0.1 Acm⁻² with a brass cathode and an Inconel anode. Electrolyses include anadditional 10 wt % H₃BO₃ which promotes uniform morphology. H₃BO₃,rather than Li₂BO, was added as a cost saving measure. H₃BO₃ uponheating releases water, and contributes the same boron oxide valencestate to the electrolyte melt as Li₂BO.

FIG. 10 presents SEM of helical carbon nanotubes after washing of theproduct, which are grown at 750° C. in a 100% Li₂CO₃ electrolyte at ahigh current density (0.5 A cm⁻²) for 2 hours on a brass/Monel cathodesusing a Chromel C (Nichrome) anode.

The composites studied in these examples included CNT-aluminum,CNT-steel, CNT-magnesium, CNT-titanium, and CNT-cement.

CONCLUDING REMARKS

It will be understood that any range of values herein is intended tospecifically include any intermediate value or sub-range within thegiven range, and all such intermediate values and sub-ranges areindividually and specifically disclosed.

It will also be understood that the word “a” or “an” is intended to mean“one or more” or “at least one”, and any singular form is intended toinclude plurals herein.

It will be further understood that the term “comprise”, including anyvariation thereof, is intended to be open-ended and means “include, butnot limited to,” unless otherwise specifically indicated to thecontrary.

When a list of items is given herein with an “or” before the last item,any one of the listed items or any suitable combination of two or moreof the listed items may be selected and used.

Of course, the above described embodiments are intended to beillustrative only and in no way limiting. The described embodiments aresusceptible to many modifications of form, arrangement of parts, detailsand order of operation. The invention, rather, is intended to encompassall such modification within its scope, as defined by the claims.

What is claimed is:
 1. A method of forming a composite material, comprising steps of: providing a high carbon footprint substance that is a metal; providing a carbon nanomaterial produced with a negative carbon-footprint indicating a net consumption of carbon dioxide during the production of the carbon nanomaterial; and forming a composite comprising the high carbon footprint substance and from 0.001 wt % to 25 wt % of the carbon nanomaterial by one of: a. heating the high carbon footprint substance and adding the carbon nanomaterial thereto; b. coating one or more individual particles of the carbon nanomaterial with a second metal and adding the coated carbon nanomaterial to the high carbon footprint material for providing an interface between the coated carbon nanomaterial and the metal; c. mixing a powder of the metal and a powder of the carbon nanomaterial and sintering the powder mixture; and d. making a suspension of the carbon nanomaterial in a solvent and mixing the suspension with a powder of the metal, treating the mixture of the suspension and the metal powder to form a powder mixture of the carbon nanomaterial and the metal, wherein the carbon nanomaterial is dispersed in the composite material to reduce the carbon dioxide emission for producing the composite material relative to the high carbon footprint substance.
 2. The method of claim 1, wherein the carbon nanomaterial comprises carbon nanofibers with an average aspect ratio of 10 to 1000 and a thickness of 3 nm to 999 nm.
 3. The method of claim 2, wherein the nanofibers comprise one or more of carbon nanotubes, helical carbon nanotubes, untangled carbon nanofibers, carbon nano-onions, a carbon nano-scaffold, a nano-platelet, and graphene.
 4. The method of claim 1, wherein the carbon nanomaterial is formed from a molten carbonate by electrolysis.
 5. The method of claim 4, wherein the molten carbonate is generated by a reaction of carbon dioxide and a metal oxide in a molten electrolyte.
 6. The method of claim 5, wherein the metal oxide is lithium oxide.
 7. The method of claim 4, wherein the molten carbonate comprises a lithium carbonate or a lithiated carbonate.
 8. The method of claim 1, wherein the metal is aluminum or alloy thereof and the step of forming the composite comprises heating the aluminum to a molten state and adding the carbon nanomaterial thereto.
 9. The method of claim 1, wherein the metal is magnesium or alloy thereof and the step of forming the composite comprises coating one or more individual particles of the carbon nanomaterial with a second metal and adding the coated carbon nanomaterial to a magnesium powder for providing an interface between the coated carbon nanomaterial and the magnesium.
 10. The method of claim 9, wherein the second metal is a transition metal.
 11. The method of claim 10, wherein the second metal is nickel or alloy thereof.
 12. The method of claim 1, wherein the step of forming the composite comprises mixing a powder of the metal and a powder of the carbon nanomaterial and sintering the powder mixture.
 13. The method of claim 12, wherein the metal is one of titanium, steel, a titanium alloy or a steel alloy.
 14. The method of claim 12, wherein the step of forming the composite comprises a step of milling the powder mixture before the step of sintering.
 15. The method of claim 12, wherein the step of sintering is spark plasma sintering.
 16. The method of claim 1, wherein the metal is copper or an alloy thereof and the step of forming the composite further comprises: a. making a suspension of the carbon nanomaterial in an aqueous solvent; b. mixing the suspension with a powder of the metal; c. treating the mixture of the suspension and the metal powder to produce a powder mixture of the carbon nanomaterial and the metal; and d. sintering the powder mixture, wherein the carbon nanomaterial is dispersed within the powder mixture.
 17. The method of claim 16, wherein the step of treating the mixture of the suspension and the metal powder comprises a step of calcinating, a step of reducing, or both.
 18. The method of claim 16, wherein the step of sintering is spark plasma sintering or microwave sintering.
 19. The method of claim 1, wherein the composite material has an enhanced mechanical strength property as compared to the metal. 